Climate change, circular economy and foodborne pathogens: assessment of pathogenic E. coli and Salmonella spp. in irrigation water in Italy

Abstract

The use of reclaimed water from wastewater treatment plants (WWTPs) in agriculture represents a sustainable way to reduce water footprint. However, outbreaks linked to the consumption of contaminated ready-to-eat food (RTE) have frequently been associated with the presence of foodborne pathogens in irrigation water. To deepen the hazard characterization of water used for crop irrigation, reclaimed and surface water samples (n=15), collected in Northern Italy in spring and summer, were analysed via Real Time PCR, before and after an enrichment treatment, to detect virulence genes of STEC (Shiga toxin producing - E. coli); EPEC (Enteropathogenic E. coli); EAEC (Enteroaggregative E. coli); EIEC (Enteroinvasive E. coli); ETEC (Enterotoxigenic E. coli) and Salmonella spp. Virulence genes of Salmonella spp. and all E. coli pathogroups were detected in 14/15 samples. 11/14 samples showed the presence of pathogenic E. coli both pre- and post-enrichment. The most detected genes were stx1, stx2, eae, followed by aggR, aaiC, ipaH, lt, stp, sth genes. Four enriched samples were positive for invA gene. Four strains were isolated from enriched samples, including one STEC (stx1+) strain and two Salmonella Veneziana strains from surface water samples, and one strain of S. Taksony from a WWTP sample. The detection of viable pathogens in irrigation water suggests that the depurative treatments may not be fully effective in eliminating pathogenic E. coli and Salmonella spp. in reclaimed water. A conditioned use of surface water is needed to reduce the pathogen input on crops. Furthermore, the higher positive signals recorded after rainfalls suggest that pathogen mobilization is linked to precipitation patterns. Since the detection of pathogenic E. coli in agricultural water is not regulated by the Italian and European legislation, except for STEC O157 in spent irrigation water, their likely presence should be adequately considered and risk-oriented, depending on climatic conditions, processing technologies and type of agricultural use.